The popular vision of the mobile industry (beyond the devices) is one of cell towers, but the backbone of the industry is backhaul! Backhaul is the connection of every cell site to the network. Without backhaul, the cell sites are useless.
The word backhaul is somewhat misleading, as it brings up thoughts of double hauling of traffic. This of course is not the case. Backhaul is simply the name applied to the connection to the network. Backhaul has been around much longer than the cellular industry. It is the connection from any point of concentration (cell site, voice switch/concentrator, data switch/router, etc.) to the network. It is the facility that connects to the line side of the router. It is the facility that connects to the network side of a switch.